1. Field of the Invention
The present invention relates mainly to a control method for storage system and a storage system.
2. Description of Related Art
As a type of a storage system connected to a computer, there are disk arrays. Disk arrays are called RAID (Redundant Arrays of Inexpensive Disks). The disk array is a storage system including a plurality of disk devices arranged in an array form and a control unit for controlling them. In the disk array, read requests (data readout requests) and write requests (data write requests) are processed at high speed by parallel operation of disk devices, and redundancy is added to data. The disk arrays are classified into five levels in accordance with the type and configuration of the added data, as disclosed in “A case for Redundant Arrays of Inexpensive Disks (RAID)”, David A. Patterson, Garth Gibson, and Randy H. Katz, Computer Science Division Department of Electrical Engineering and Computer Sciences, University of California Berkeley. By the way, disk devices are storages having a hard disk, an optical magnetic disk, or the like.
On the other hand, in disk devices, there are some types differing in interface used for connection to other devices. For example, there are disk devices (hereafter referred to as FC disk devices) each having a fibre channel (hereafter referred to as FC) interface for which standardization work is being conducted by ANSI T11, and disk devices (hereafter referred to as ATA disk devices) each having an ATA (AT Attachment) interface for which standardization work is being conducted by ANSI T13.
ATA disk devices are comparatively inexpensive and used in desktop computers for homes. On the other hand, FC disk devices are used in business servers of which reliability is required. As compared with the ATA disk devices, therefore, the FC disk devices have higher processing performance in data input/output (hereafter referred to as I/O) and such higher reliability that they can withstand continuous operation over 24 hours on 365 days. In the case where these disk devices are used in storage systems such as disk arrays, disk devices are used properly sometimes in accordance with the performance, price or the like required of the disk array. For example, a technique of improving the reliability of data stored in a disk array by using a disk device that is higher in performance than a data storing disk device as a disk device for storing parities, which are redundant data, is disclosed in JP-A-10-301720.